Shafts that transmit torques and have gears arranged on the shafts are very common in transmission manufacturing. There are a large number of options for attaching these gears to the shaft, whereby the types of connections are generally subdivided into elementary shaft-hub joints and combined shaft-hub joints.
The elementary shaft-hub joints comprise form-locking connections, such as the spline shaft connection, the kerf tooth connection, the involute profile connection, the polygon profile connection, the fitted key connection and the pin connection; the force-fitting connections, such as the crimp connection and the shrink-fit, the keyed joint, the clamping ring connection, the jockey pulley connection and the star washer connection; and the materially engaging connections, such as the welded connection, the soldered connection, and the glued connection.
The combined shaft-hub-joint connections include non materially-engaging connections, such as the pressure knurl connection and the pressure point closure connection; non-materially engaging/materially-engaging connections, such as the pressure adhesion connection, the pressure-soldering connection and the pressure welding connection; and materially engaging connections, such as the soldering-welding connections, for example.
The types of known connections described above are characterized by the disadvantage that movement of the components or, as the case may be, the gears on the shaft is not prevented. Despite optimized design, microscopic movements do occur, for example, due to load peaks. This kind of movement of the gears on the shafts must be avoided at all costs, particularly in transmissions in which exact alignment of gear teeth of different gears in relation to each other plays a decisive role. This is particularly the case in transmissions with load distribution between two or more countershafts; here, absolute placement precision is required throughout the lifetime of the transmission.
In order to resolve the problem cited above, DE 196 20 330 A1 proposes a shaft-hub-joint connection for a component on a shaft in which, on the one hand, the component is shrunk-fit to the shaft and, on the other, in which it is also held in place by means of a form-locking connection, in order to avoid movement. More precisely, the cited document proposes to attach a gear to the shaft by means of a shrink-fit and to provide a pin-shaped element that extends, on the one hand, into the shaft and, on the other, into the gear, to obtain a form-locking connection.
An additional permanent shaft-hub connection is known from DE 103 19 629 A1 in which the gear is attached by means of a shrink-fit to the shaft, i.e. by means of shrink-fitting. The cited document also proposes that immediately adjacent gears partially overlay each other, in which case the adjacent regions of the gears are also connected by means of a shrink-fit.
The shaft-hub connections known from the previous documents comprise gears with an axial first section that has external cogging and an axial second section that has no gear teeth. Shrink-fitting these gears to the shaft causes shrinkage stress that is superimposed on the stress on the bases of the gear teeth, so that a multi-axial stress-state arises in the first section. In the worst possible case, this multi-axial stress-state can lead to a break in one or more of the gear teeth of the cogging. For this reason, the practice has been modified so that in the axial first section, which is provided with the cogging, a weaker shrink-fit is produced than is produced in the axial second section, so that there is less shrinkage stress in the axial first section. In this way, through a reduction in the shrinkage stress in the axial first section, damage to the cogging from superposition of stress can be avoided. This measure has the disadvantage, however, of reducing the maximum torque that can be transmitted from the gear to the shaft.